FunctionBinds tightly to hydroxyapatite. Appears to form an integral part of the mineralized matrix. Probably important to cell-matrix interaction.Acts as a cytokine involved in enhancing production of interferon-gamma and interleukin-12 and reducing production of interleukin-10 and is essential in the pathway that leads to type I immunity.

Tissue specificityBone. Found in plasma.

Sequence similaritiesBelongs to the osteopontin family.

Post-translationalmodificationsExtensively phosphorylated on clustered serine residues.N- and O-glycosylated.Phosphorylation sites are present in the extracelllular medium.